Chinese activists and dissidents see the United States President’s visit to China as an opportunity to highlight their causes—but it comes with a risk. Several of them were already arrested last week before Barack Obama arrived in Shanghai yesterday (Sunday).  The United States President will spend the rest of his four-day trip in Beijing.

Among those detained was Zhao Lianhai. He’s an advocate for parents of children who were poisoned by melamine-tainted milk. Mr. Zhao’s own three-year-old son was poisoned by the toxic milk and he’s been campaigning ever since the scandal was exposed last year.

According to activist group Human Rights in China, Zhao was taken from his home on Friday at 10:30 p.m. by about a dozen police officers from Beijing’s Daxing District Public Security Bureau and Tuanhe substation. When Zao resisted, police officers accused him of "provoking an incident" in the summons.

Another activist, Qi Zhiyong was also detained. He lost his left leg during the Tiananmen Square massacre in 1989. He’s been persistently speaking up for victims of the massacre for many years.

Last Monday, (November 9) Qi tried to organize a human rights seminar at a park in Beijing that would have lasted until the end of Obama’s visit. Qi told AFP he was charged with (quote), “unlawful assembly and disturbing the social order.” He’s being held in the Beijing suburbs.

Qi said two other well-known dissidents are also being detained: Li Jinping who tries to organize annual commemorations for ousted former leader Zhao Ziyang; and a housing rights activist, Yang Qiuyu.

Qi told AFP he knows of at least 30 other activists who were detained ahead of Obama’s visit.